The art of surveying and mapping has dramatically changed through the use of satellite navigation equipment. Satellite survey devices include receivers that receive position signals from the global positioning system (GPS), Global Navigation Satellite System (GLONASS) receiver or other satellite or pseudolite systems. The position signals are used to compute the position of the receiver.
While selective availability (S/A) and environmental conditions may degrade the position signals to 100 meter accuracy, differential correction (DGPS) and real time kinematic (RTK) processes may be employed increase accuracy to the within 1 to 2 centimeter accuracy. RTK and real time computation of DGPS both require the use of an additional radio frequency receiver for reception of additional data that is used to compute a corrected, more accurate, position. Thus, the satellite survey device which is typically called the "rover device", includes a range pole for identifying the point for which a location is to be computed, a user input/output device for entry and display of information and data, a satellite receiver and a radio receiver.
The range pole has attached to it an antenna for receiving GPS signals and a circular level or vial. The user holds the range pole and moves the range pole about until the level indicates that the range pole is vertically oriented and the bottom of the pole touches a location to be surveyed. Once vertically oriented, the information received via the GPS antenna can be used to accurately compute the position of the location. Typically, the user will have a backpack that includes a wireless link, such as a radio modem, for receiving additional data, e.g., correction signals, from a reference station, e.g., a differential GPS (DGPS) base station. Using DGPS technology, more precise measurements are obtained. The backpack also contains equipment and circuits for generating positional information based upon the signals received through the antenna and the wireless link. The data collection device enables the user to make manual entries, and also provides a visual reading of the survey measurements obtained.
A typical method of navigating to a known position will now be described. The user navigates to a location of interest by inputting the desired position in latitude and longitude (or any convenient x, y, z coordinate system) to the survey device and then following on screen directions such as an indication of the direction and distance from the user's current position. The on screen indications are useful while the user is approaching the location of interest from a distance; however, the on screen indication may change wildly when the user is very close to the desired position. Therefore, once the user is within a few meters, the user's pace must be slowed to assure the point is not passed over. When the user has identified an estimated location that is believed to be the location of interest, the process of confirming the estimated location may begin. This iterative process typically involves placing the range pole over the estimated location, leveling the range pole, receiving a measurement, and adjusting the placement of the range pole. This confirmation process continues until the measurement received matches the position of the location of interest. After receiving feedback from the input/output device the user adjusted the placement of the range pole to another location. Upon receiving the second measurement, the user adjusted the placement of the range pole to yet another location. At this point, the user received confirmation that the range pole was in fact positioned over the desired location.
Land seismic surveys are commonly performed using vibroseis trucks with these trucks providing the seismic energy. The trucks vibrate at predetermine points that are usually marked with stakes that have been placed by surveyors. During operations, the vibroseis trucks navigate from point to point using these survey stakes. One problem with using survey stakes is that they can be destroyed or removed by things such as cattle, vehicles, and vandals. Another problem is the cost associated with the survey stake out. In addition, the vibroseis trucks used in these operations are very large and make frequent short moves while in formation with other trucks. Due to these and other problems, some vibroseis trucks have on board navigation systems. However, if drivers of these trucks have to divert their attention from the safe steering of the trucks to read a navigation display console, unsafe conditions resulting in accidents may occur.